Gv3113061312

Alok Vyas, Dr. Alka Bani Agrawal / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 1, January -February 2013, pp1306-1312
Offset-Strip Fin Heat Exchangers A Conceptual Review Study
ALOK VYAS *, Dr. Alka Bani Agrawal **
*(Department of Mechanical Engineering, Rajeev Gandhi Proudyogiki Vishwavidyalaya, Bhopal (M.P.) –
462038)
**(Department of Mechanical Engineering, Rajeev Gandhi Proudyogiki Vishwavidyalaya, Bhopal (M.P.) –
462038)

Abstract
This paper is a review of research work The geometry of the offset strip fin surface is
of last few years on heat transfer growth in described by the following parameters:
offset-strip fin heat exchangers. It features a (i) Fin spacing (s), excluding the fin thickness,
broad discussion on the application of enhanced (ii) Fin height (h), excluding the fin thickness,
heat transfer surfaces to offset strip fin heat (iii) Fin thickness (t), and
exchangers. In this paper we are discussing 2D (iv) The strip length (_), in the flow direction.
& 3D Analysis in OSF, Experimental & The lateral fin offset is generally uniform
investigating research on OSFs, Analytical model and equal to half the fin spacing (including fin
to predict the heat transfer coefficient and the thickness). Figure shows a schematic view of the
friction factor of the OSFs geometry, Heat rectangular offset strip fin surface and defines the
transfer and pressure drop Characteristics of an geometric parameters. The following are some
OSFs Thermal performance, CFD Analysis on commonly used secondary parameters derived from
OSFs. the basic fin dimensions

Keywords - CFD Analysis, Offset-strip fin, Heat
transfer growth, laminar and turbulent flow.

INTRODUCTION
The first sign of movement to relatively
“compact” heat exchangers was seen in the
automotive industry in the early 1900’s, when an
improved manner for removing heat from engines
with minimal material (weight) was sought.
Whereas heat was previously removed from engines
by boiling a collection of water and releasing it into Fig.1Offset-strip fin Geometry
the air in an unsophisticated convection process,
heat exchangers were seen as an inexpensive way to
improve engine performance (Shah & Sekulic,
1. Two & Three Dimensional analysis in
2003).[1] OSFs Heat Exchangers
The offset strip fin is one of the most Patankar and Prakash [2] presented a two
widely used finned surfaces, particularly in high dimensional analysis for the flow and heat transfer
effectiveness heat exchangers employed in in an interrupted plate passage which is an
cryogenic and aircraft applications. These fins are idealization of the OSFs heat exchanger. The main
created by cutting a set of plain rectangular fins aim of the study is investigating the effect of plate
periodically along the flow direction, and shifting thickness in a non-dimensional form t/H on heat
each strip thus generated by half the fin spacing transfer and pressure drop in OSF channels because
alternately left and rightward. the impingement region resulting from thick plate
The flow is thus periodically interrupted, on the leading edge and recalculating region behind
leading to creation of fresh boundary layers and the trailing edge are absent if the plate thickness is
consequent heat transfer improvement. Interruption neglected. Their calculation method was based on
of flow also leads to greater viscous pressure drop, the periodically fully developed flow through one
manifested by a higher value of effective friction periodic module since the flow in OSF channels
factor. In addition to the effect of wall shear, attains a periodic fully developed behaviour after a
resistance to flow also increases due to form drag short entrance region, which may extend to about 5
over the leading edges of the fin sections facing the (at the most 10) ranks of plates (Sparrow, et al.
flow, and due to trailing edge vortices. The effective 1977). Steady and laminar flow was assumed by
heat transfer coefficient and friction factor are them between Reynolds numbers 100 to 2000. They
composite effects of the above mechanisms. found the flow to be mainly laminar in this range,
The Offset Strip Fin Geometry although in some cases just before the Reynolds no.
2000 there was a transition from laminar to

1306 | P a g e

turbulence. Specially for the higher values of t/H. from 10 to 2000 in both the papers. The results of
They used the constant heat flow boundary the two studies showed that the Prandtl number has
condition with each row of fins at fixed temperature. a significant effect on heat transfer in OSF
They made their analysis for different fin thickness channel.Although there is no effect on the pressure
ratios t/H= 0, 0.1, 0.2, 0.3 for the same fin length drop.
L/H = 1, and they fixed the Prandtl number of fluid Zhang et al [7] investigated the
= 0.7. For proper validation they compared there mechanisms for heat transfer enhancement in
numerical results with the experimental results of parallel plate fin heat exchangers including the
[London and Shah][1] for offset strip fin heat inline and staggered arrays of OSFs. They have also
exchangers. The result indicated reasonable taken into account the effect of fin thickness and the
agreement for the f factors, but the predicted j factor time dependent flow behavior due to the vortex
was twice as large as the experimental data. They shedding by solving the unsteady momentum and
concluded that the thick plate situation leads to energy equation. The effects of vortices which are
significantly higher pressure drop while the heat generated at the leading edge of the fins and travel
transfer does not sufficiently improve despite the downstream along the fin surface was also studied.
increased surface area and increased mean velocity. From there study they found that only the surface
Fangjun Hong & Ping Cheng [3] show the 3-D interruptions increase the heat transfer because they
numerical simulation, taking into consideration the cause the boundary layers to start periodically on fin
conjugate heat transfer of heat sink base material surfaces and reduce the thermal resistance to
and coolant, was conducted for laminar forced transfer heat between the fin surfaces and fluid.
convection of water to study offset strip fin micro However after a critical Reynolds number the flow
channel heat sink for microelectronic cooling. It is becomes unsteady and in this regime the vortices
found that due to the periodical change of the flow play a major role to increase the heat transfer by
direction, the convective heat transfer is enhanced bringing the fresh fluids continuously from the main
by mixing the cold and hot coolant, and the stream towards the fin surface.
periodical breakup of boundary layer is another Dejong et al [8] carried out an experimental
factor to enhance heat transfer. The effects of the and numerical study for understanding the flow and
ratio of fin interval to fin length K, and fin numbers heat transfer in OSFs. In the study the pressure drop,
M on the performance of strip-fin micro channel local Nusselt number, average heat transfer and skin
were also investigated. It is found that for the same friction coefficient on fin surface, instantaneous
K, with the increase of M, the required mass flow flow structures and local time averaged velocity
rate to keep the maximum wall temperature profiles in OSF channel were investigated. They
decreases. compared there results with the experimental results
obtained by Dejong and Jacobi [1997] and unsteady
2. Experimental & investigating research on numerical simulation of Zhang et al [1997]. There
OSFs results indicate that the boundary layer
Manglik and Bergles[4] carried an development, flow separation and reattachment,
experimental research on OSFs. They investigated wake formation and vortex shedding play an
the effects of fin geometries as non dimensional important role in the OSF geometry.
forms on heat transfer and pressure drop, for their S.YoucefAli_,J.Y.Desmons[9] Presented
study they used 18 different OSFs. After their A mathematical model that allows the
analysis they arrived upon two correlations, one for determination of the thermal performances of the
heat transfer and another one for pressure drop. The single pass solar air collector with offset rectangular
correlations were developed for all the three regions. plate fin absorber plate is developed (fig.2). The
They compared there results from the data obtained model can predict the temperature profile of all the
by other researchers in the deep laminar and fully components of the collector and of the air stream in
turbulent regions. There correlations can be the channel duct.the offset rectangular plate fins
acceptable when comparing the results of the were introduced, which increase the thermal heat
expressions to the experimental data obtained by transfer between the absorber plate and the fluid.
Kays and London [5]. The offset rectangular plate fins, mounted in a
Hu and Herold [6] presented two papers to staggered pattern, are oriented parallel to the fluid
show the effect of Prandtl no. on heat transfer and flow and are soldered to the underside of the
pressure drop in OSF array. Experimental study was absorber plate. They are characterized by high heat
carried out in the first paper to study the effect for transfer area per unit volume and generate the low
which they used the seven OSFs having different pressure losses. The experimental results of the air
geometries and three working fluids with different stream temperature will be compared with the
Prandtl number. At the same time the effect of
changing the Prandtl number of fluid with
temperature was also investigated. The study was
carried out in the range of Reynolds number varying

1307 | P a g e

results obtained by the theoretical model suggested

Fig.3(a) Laminar flow on the fins and in the wakes
Fig. 2 Experimental setup (Source Joshi and Webb 1987)
The model, which determines the thermal
performances of this collector and temperatures of
all its components and air stream, uses an equation
of global irradiance incident along the collector,
ambient and inlet collector temperature. Predicted
and experimental results of the air stream
temperature are in good agreement particularly in
the transition flow regime. On the other hand, in the
laminar flow system, the greatest recorded variation,
which is of 71ↄC obtained for the lowest value of
the Reynolds number Re ¼ 479. In this same case,
the difference between the theoretical and the
experimental air stream temperature at the collector Fig.3(b) Laminar flow on the fins and oscillating
exit is only of 41 ↄC which is acceptable. flow on the wakes
(Source Joshi and Webb 1987)
3. Analytical model to predict the heat
transfer coefficient and the friction factor of Four different flow regimes were identified
the OSFs geometry by Joshi and Webb [12] from their experiment. The
Joshi and Webb [10] developed an flow was found to be laminar and steady in the first
analytical model to predict the heat transfer regime. In the second regime the oscillating flow
coefficient and the friction factor of the offset strip structures were found in the transverse direction.
fin surface geometry. To study the transition from The flow oscillated in the wake region between two
laminar to turbulent flow they conducted the flow successive fins in the third regime. And in the fourth
visualization experiments and an equation based on regime the effect of vortex shedding came into
the conditions in wake was developed. They also picture. The laminar flow correlation of Joshi and
modified the correlations of Weiting [11]. There Webb started to under predict the j and f factors at
was some difference between there correlation. Four the second regime. So they assumed the Reynolds
different flow regimes were identified by Joshi and number at that point as the critical Reynolds number
Webb [12] from there experiment. The flow was to identify the transition from laminar to turbulent.
found to be laminar and steady in the first regime. In
the second regime the oscillating flow structures 4. Heat transfer and pressure drop
were found in the transverse direction. The flow Characteristics of an OSFs
oscillated in the wake region between two H. Bhowmik and Kwan-Soo Lee [13]
successive fins in the third regime. And in the fourth studied the heat transfer and pressure drop
regime the effect of vortex shedding came into characteristics of an offset strip fin heat exchanger.
picture. The laminar flow correlation of Joshi and For their study they used a steady state three
Webb started to under predict the j and f factors at dimensional numerical model. They have took water
the second regime. So they assumed the Reynolds as the heat transfer medium, and the Reynolds
number at that point as the critical Reynolds number number (Re)in the range of 10 to 3500. Variations in
to identify the transition from laminar to turbulent. the Fanning friction factor f and the Colburn heat
transfer j relative to Reynolds number were
observed. General correlations for the f and j factors
were derived by them which could be used to
analyze fluid flow and heat transfer Characteristics
of offset strip fins in the laminar, transition, and
turbulent regions of the flow.

1308 | P a g e

heat transfer coefficient. They also derived the j
factor and f factor by using regression analysis.
Results showed that the heat transfer coefficient and
pressure drop reduce with enlarging the fin space,
fin height and fin length.
Michna et al [16] investigated the effect of
increasing Reynolds number on the performance of
OSFs. He conducted the experiment at Reynolds
number between 5000 to 120000 and found that
both heat transfer and pressure drop increased with
increasing Reynolds number, because the effect of
vortex shedding and eddy formation at turbulent
regime. Operation of OSF heat exchangers under
Fig.4 Direction of fluid at LPD & HPD this Reynolds number may be useful in systems
where minimizing the heat exchanger size or
Saidi and Sudden [14] carried out a maximizing the heat transfer coefficient is more
numerical analysis of the instantaneous flow and important than minimizing the pressure drop.
heat transfer for OSF geometries in self-sustained Various experiments are carried out in
time-dependent oscillatory flow. The effect of order to find out the j and f factors of the various
vortices over the fin surfaces on heat transfer was heat exchangers and are called as the thermal
studied at intermediate Reynolds numbers where the performance testing. These testing are needed for
flow remains laminar, but unsteadiness and vortex heat exchangers, which do not have reported j and f
shedding tends to dominate. They compared their data. Therefore, this test is conducted for any new
numerical results with previous numerical and development or modification of the finned surfaces.
experimental data done by Dejong, et al. (1998). T. Lestina & K. Bell, Advances in Heat Transfer,
told for heat exchangers already existing in the
plants this test is done for the following reasons:
a) Comparison of the measured performance with
specification or manufacturing design rating data.
b) Evaluation of the cause of degradation or
malfunctioning.
c) Assessment of process improvements such as
those due to enhancement or heat exchanger
replacement.
Another reason for developing these
correlations is that, generally in most heat exchanger
problems the working fluid, the heat flow rate and
Fig. 5. Heat transfer in offset plate fins mass flow rate are usually known, so if certain
correlations between geometry and fin performance
The studies of few researchers like is also known, then the problem can be deeply
Patankar and Prakash [1], Kays and London [5] it is simplified. For that purpose developing the
easy to get information regarding the effects of correlations for fanning friction factor f and
OSFs on heat transfer and pressure drop. But most Colbourn factor j are important for heat
of the researchers have not taken into account the exchanger.These are the ratio of free flow area (
effect of manufacturing irregularities such as burred = s/h), the ratio of heat transfer area (β= t/l), and the
edges, bonding imperfections, separating plate ratio of fin density (y= t/s).
roughness which also affect the heat transfer and Show in Fig.1
flow friction characteristics of the heat exchanger.
Dong et al [15] made experiments and analysis 5. Thermal performance of OSF Heat
considering the above factors to get better thermal
Exchangers
and hydraulic performance from the OSFs. Sixteen
S. Youcef-Ali_, J.Y. Desmons [17] A
types of OSFs and flat tube heat exchangers were
mathematical model that allows the determination of
used to make the experimental studies on heat
the thermal performances of the single pass solar air
transfer and pressure drop characteristics. A number
collector with offset rectangular plate fin absorber
of tests were made by changing the various fin
plate is developed. The model, which determines the
parameters and all the tests were carried out in
thermal performances of this collector and
specific region of air side Reynolds number (500-
temperatures of all its components and air stream,
7500), at a constant water flow crate. The thermal
uses an equation of global irradiance incident along
performance data was analyzed using the
the collector, ambient and inlet collector
effectiveness-NTU method in order to obtain the

1309 | P a g e

temperature. Predicted and experimental results of railway industry (Shah, McDonald, & Howard,
the air stream temperature are in good agreement 1980).[21] The 1980’s brought an increase in
particularly in the transition flow regime. computing power and function that led compact heat
exchanger research away from experimental
Suzuki et al [18] in order to study the solutions in favor of Computational Fluid Dynamics
thermal performance of a staggered array of vertical (CFD). CFD provided low-cost means to simulate
flat plates at low Reynolds number has taken a the physics occurring inside heat exchangers
different numerical approach by solving the elliptic relatively accurately, without the need to construct
differential equations governing the flow of and test physical apparatus before a final design was
momentum and energy. The validation of their developed.
numerical model has been done by carrying out
experiments on a two dimensional system, followed
by those on a practical offset strip fin heat
exchanger. The experimental result was in good
agreement with the performance study for the
practical offset-strip-fin type heat exchanger in the
range of Reynolds number of Re<800.
Tinaut et al [19] developed two correlations
for heat transfer and flow friction coefficients for
OSFs and plane parallel plates. The working fluid
for OSF was engine oil and water was taken for
analyzing the parallel plate channels. By using the
correlations of Dittus and Boelter and some
expressions of Kays and Crawford they obtained
their correlations. For the validation of their results
they compared there correlations with correlations
of Weitng[6]. Fig. 6. CFD Analysis in offset plate fins
Although their were some differences
It took several years, and decades in some
between the results but there correlations have been
cases, for the computing power to be able to
found acceptable upon comparing their results to
the data obtained from other correlations. accurately predict the physics in a timely fashion for
Randall.F.Barron[20], shows that the incredibly small geometries in compact heat
Cryogenic heat exchanger, has showed the effect of exchangers. That breakthrough allowed for
significant advancements in the industry.
longitudinal wall heat conduction on the
Optimization processes were more easily obtained,
performance of cryogenic heat exchangers.
and more complex geometries could be tested with
Cryogenic heat exchangers operate at low
temperatures where the longitudinal wall heat the use of CFD.The Fig.6& 7 Shows the CFD
Analysis in different field Fig.5 show fluid flow in
conduction results in serious performance
deterioration this is because they have small OSFs geometry and Fig.6 shows that (a) velocity
distances ( on the order of 100 to 200 mm or 4 to 8 field, (b) Velocity distribution, and (c) temperature
field in OSFs geometry.
in) between the warm and cold ends i.e. they have
short conduction lengths. Because of the natural
requirement of high effectiveness for cryogenic heat
exchangers, the NTU values are usually large (as
high as 500 to 1000), so the effect of longitudinal
conduction is most pronounced for heat exchangers
having short conduction lengths and large NTU. The
wall longitudinal heat conduction reduces the local
temperature difference between the two streams,
thereby reducing the heat exchanger effectiveness
and the heat transfer rate.

6. CFD Analysis
Heat exchanger designs continued to
expand and develop through the 1960’s and more
industries gained interest in using compact heat Fig. 7. CFD Analysis in offset plate fins (a)
Velocity field (b) velocity distribution (c)
exchangers to increase efficiency. Compact heat
Temperature field
exchanger technologies spread from the automotive
industry to the air conditioning industry, several
manufacturing industries, and even to the magnetic

1310 | P a g e

In the time since CFD became prevalent in Flow and Heat transfer in Interrupted Plate
heat exchanger design, several systems of passages. International Journal of Heat
commercial codes have been developed to allow for and Mass Transfer 24:1801-1810
rapid testing and simulations. The programs 3. Fangjun Hong & Ping Cheng Three
continue to become more accurate, and as dimensional numerical analyses and
computers continue to become more powerful and optimization of offset strip-fin micro-
swift in their calculations, the use of CFD will channel heat sinks International
expand to new applications. Communications in Heat and Mass
The technologies available today are leaps Transfer volume36,issue-
and bounds ahead of the resources available to those 7,August2009,Pages 651–656
designing the MSBR in the 1960’s. Computing 4. Manglik and Bergles A. E. 1995 Heat
power has made hydrodynamics and heat transfer Transfer and Pressure drop Correlations for
incredibly more accurate in comparison to hand Rectangular Offset Strip Finn Compact
drawings and manual calculations done in the initial Heat Exchangers. Experimental Fluid
MSBR design (Bettis, et al., 1967). The computer Science 10:171-180.
programs developed at ORNL for optimization of 5. Kays, W. M. and London, A. L. Compact
the heat exchanger designs were rudimentary Heat Exchangers, McGraw-Hill, New York
compared to the commercial software packages (1984)
available today. Performing CFD analyses in 6. Hu S and Herold K. E. 1995a Prandtl
FLUENT, with automated optimization available in Number Effect on Offset Strip Fin Heat
ANSYS Workbench, is much more sophisticated Exchanger Performance: Predictive Model
than the analog computer models used in the 1960’s for Heat Transfer and Pressure Drop.
for overall plant operation (Burke, 1972) and heat International Journal of Heat and Mass
exchanger design (Bettis, Pickel, Crowley, Simon- Transfer 38(6) 1043-1051 Hu S and Herold
Tov, Nelms, & Stoddart, 1971). K. E. 1995b Prandtl number Effect on
Offset Strip Fin Heat Exchanger
CONCLUSION Performance: Experimental Results.
This paper gives a detailed description of International Journal of Heat and Mass
OSFs types of geometries that can be used to Heat Transfer 38(6) 1053-1061.
transfer. Offset-strip-fin enhancement geometries 7. Zhang L. W., Balachandar S., Tafti D. K.
have been developed in order to make heat and Najjar F. M. 1997. Heat Transfer
exchangers more efficient and compact. Currently Enhancement Mechanisms in Inline and
plate-fin heat exchangers are very common in Staggered Parallel Plate Fin Heat
cryogenic systems and gas-liquefaction plants. Exchanger. International Journal of Heat
Increased demand for smaller and better heat and Mass Transfer 40(10):2307-2325
exchange devices will certainly lead to more 8. Dejong N. C., Zhang L. W., Jacobi A. M.,
widespread use of plate-fin heat exchangers in other Balchandar S. and Tafti D. K.
applications as well. 1998.AComplementaryExperimental and
This review paper discuses the considerable Numerical Study of Flow and Heat
experimental, Numerical and CFD work which has Transfer in Offset Strip Fin Heat
been done on heat transfer growth through offset- Exchangers. Journal of Heat Transfer
strip fin experimental work. There is a need of 12:690:702
analyzing dynamics similarities amongst the 9. S.YoucefAli_,J.Y.Desmons,Numerical and
geometrical similarities on large scale model experimental study of a solar equipped
covering industrial application, Further research is with offset rectangular plate fin absorber
required to be conducted at a large scale on plate Volume 31, Issue 13, Pages 2025-
considerable range of curvature ratio, low range of 2206 (October 2006) Renewable Energy an
curvature ratio, low range of Prandtl number and InternationalJournal,http://www.sciencedir
Reynolds numbers temperature etc. ect.com/science/journal/09601481
10. Joshi H. M. and Webb R. L. 1987. Heat
REFERENCES Transfer and Friction in Offset Strip Fin
1. London, A. L. A Brief History of Compact Heat Exchanger, International Journal of
Heat Exchanger Technology, in R. K. Heat and Mass Transfer. 30(1): 69-80
Shah, C. F. McDonald and C. P. Howard 11. Wieting, A. R. Empirical Correlations for
(Eds), Compact Heat Exchanger – Heat Transfer and Flow Friction
History, Technological Advancement and Characteristics of Rectangular Offset-Fin
Mechanical Design Problems, HTD, 10, Plate-Fin Heat Exchangers ASME J. Heat
ASME, 1-4, (1980) Transfer 97 488-490 (1975)
2. Patankar S. V. and Prakash C. 1981 An 12. Joshi, H. M. and Webb, R. L. Heat
Analysis of Plate Thickness on Laminar Transfer and Friction of the Offset Strip-fin

1311 | P a g e

Heat Exchanger Int. J. Heat Mass Transfer
30(1) 69-84 (1987)
13. H. Bhowmik and Kwan-Soo 2009.
Analysis of Heat Transfer and Pressure
DropCharacteristics in an Offset Strip Fin
Heat Exchanger. International Journal of
Heat and MassTransfer 259-263
14. Saidi A. and Sudden B. 2001. A Numerical
Investigation of Heat Transfer
Enhancement in Offset Strip Fin Heat
Exchangers in Self Sustained Oscillatory
Flow. International Journal of Numerical
Methods for Heat and Fluid Flow. 11(7):
699-716
15. Dong J., Chen J., Chen Z. and Zhou Y.
2007. Air Side Thermal hydraulic
Performance of Offset Strip Fin Heat
Exchangers Fin Alumunium Heat
Exchangers. Applied Thermal Engineering
27:306-313
16. Michna J. G., Jacobi A. M. and Burton L.
R. 2005. Air Side Thermal- Hydraulic
Performance of an Offset Strip Fin Array at
Reynolds Number up to 12, 0000. Fifth
International Conference on Enhanced
Compact and Ultra Compact Heat
Exchangers. Science, Engineering and
Technology 8-14.
17. S. Youcef-Ali_, J.Y. Desmons Numerical
and experimental study of a solar equipped
with offset rectangular plate fin absorber
plate Volume 31, Issue 13, Pages 2025-
2206 (October 2006) Renewable
EnergyanInternationalJournal,http://www.
sciencedirect.com/science/journal/0960148
1
18. Suzuki, K., Hiral, E., Miyake, T.,
Numerical and Experimental studies on a
two Dimensional Model of an Offset-Strip-
Fin type Compact Heat Exchanger used at
low Reynolds Number. International
Journal of Heat and Mass Transfer 1985
28(4) 823-836
19. Tinaut F. V., Melgar A. and Rehman Ali
A. A. 1992 Correlations for Heat Transfer
and Flow Friction Characteristics of
Compact Plate Type Heat Exchangers.
International Journal of Heat and Mass
Transfer. 35(7):1659:166
20. Barron R. F., Cryogenic Heat Transfer,
Taylor and Francis (1999) 311-318.
21. R. K. Shah, C. F. McDonald and C. P.
Howard (Eds), Compact Heat Exchanger –
History, Technological Advancement and
Mechanical Design Problems, HTD, 10,
ASME, 1-4, (1980)

1312 | P a g e

Gv3113061312

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (15)

Destacado

Destacado (20)

Similar a Gv3113061312

Similar a Gv3113061312 (20)

Último

Último (20)

Gv3113061312